The present invention relates to an automobile roof reinforcement member extending in the vehicle lateral direction under an automobile roof panel and, more particularly, to an automobile roof reinforcement member made of extruded aluminum alloy highly deformation resistant under an axial compressive load (applied in the longitudinal direction of the roof reinforcement member).
An automobile roof reinforcement member (hereinafter also referred to simply as a “roof reinforcement member) is installed in proximity to a roof panel member of an automobile such that it extends in the vehicle lateral direction with each end portion thereof in the vehicle lateral direction joined to a frame part, for example, a body side panel or a center pillar included in the corresponding side of the vehicle body either directly or via a bracket provided in the end portion. This is to secure rigidity and strength in the vehicle lateral direction of the roof reinforcement member and also to secure dent resistance and tensile rigidity of the roof panel member.
With the side crash standard for vehicles intensified in recent years, automobile roof reinforcement members have come to be required to have high strength against deformation caused by a compressive load applied, from a vehicle side, in the vehicle lateral direction. What is generally done to enhance the strength against axial compression of a roof reinforcement member is to form a closed sectional part in the roof reinforcement member. Aluminum alloy for extrusion is suitable for forming a shape having a closed sectional part while also being suitable to form light-weight items. Hence, various cross-sectional shapes having a closed sectional part of roof reinforcement members have been proposed (refer to, for example, Japanese Patent Laid Open Nos. 2003-112656, 2006-240420, and 2006-240543).
As stated in Japanese Patent Laid Open No. 2006-240543, the strength against axial compression of a roof reinforcement member is defined by the axial compressive load that causes the roof reinforcement member subjected to the load to start bending upward or downward. Namely, to increase the strength against deformation caused by axial compression of a roof reinforcement member, it is most effective to increase the strength against upward/downward bending of the roof reinforcement member.
As shown in FIG. 8, an extruded aluminum alloy part disclosed in Japanese Patent Laid Open No. 2006-240543 includes, as seen in a cross-section thereof perpendicular to the direction in which the aluminum alloy part was extruded, a pair of upper and lower flanges 1 and 2 approximately parallel-facing each other and a pair of webs 3 and 4 formed approximately perpendicularly to the flanges 1 and 2. The flanges 1 and 2 and webs 3 and 4 form an approximately rectangular closed sectional part 5. The flanges 1 and 2 each project, in the vehicle longitudinal direction, forward and rearward from the closed sectional part 5 thereby forming projecting flange portions 1a, 1b, 2a, and 2b, respectively. The extruded aluminum alloy part having the above described cross-sectional shape, i.e. including the flanges 1 and 2 with portions projecting from the closed sectional part 5, has higher strength against upward/downward bending than an extruded aluminum alloy part having a closed sectional part only without any projecting portion, provided that the two extruded aluminum alloy parts have an equal cross-sectional area (refer to paragraph 0025 of Japanese Patent Laid Open No. 2006-240543).